Generally, an electrophotographic printing machine includes a photoconductive member which is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to an optical light pattern representing a document being produced. This records an electrostatic latent image on the photoconductive member corresponding to informational areas contained within the document. After the electrostatic latent image is formed on the photoconductive member, the electrostatic latent image is developed by bringing a developer material into proximal contact therewith. Typically, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted to the electrostatic latent image from the carrier granules and form a powder image on the photoconductive member which is subsequently transferred to a copy sheet. Finally, the copy sheet is heated or otherwise processed to permanently affix the powder image thereto in the desired image-wise configuration.
In the prior art, both interactive and non-interactive development has been accomplished with magnetic brushes. In typical interactive embodiments, the magnetic brush is in the form of a rigid cylindrical sleeve which rotates around a fixed assembly of permanent magnets. In this type of development system, the cylindrical sleeve is usually made of an electrically conductive, non-ferrous material such as aluminum or stainless steel, with its outer surface textured to improve developer adhesion. The rotation of the cylindrical sleeve transports magnetically adhered developer through a development zone where there is direct contact between the magnetic brush and an imaged surface, and toner is stripped from passing magnetic brush filaments by electrostatic fields of an image.
A commonly used development technique involves a single component developer material, comprised mainly of toner particles. In a typical single component development system, each toner particle has both magnetic properties (to allow the toner particles to be magnetically conveyed to an imaging member) and an electrostatic charge (to enable the toner particles to adhere to the imaging member). In such a system, a developer roll is in the form of a cylindrical sleeve which rotates about a stationary magnet assembly. The magnetized toner particles adhere to the rotating cylindrical sleeve by the force of stationary magnets with the cylindrical sleeve.
In a single component development system, the toner particles are charged by a charge-metering member or a trim blade. The charge-metering member is typically in continuous contact with the toner particles along one portion or longitude of the developer roll. The charge-metering member performs two simultaneous functions: it allows a uniform metered layer of toner particles to pass underneath, and uniformly charges the toner particles that are mechanically metered. That is, the action of the toner particles rubbing against the charge-metering member and each other while being metered by the charge-metering member induces a charge on the toner particles. The uniformity of a nip formed between the charge-metering member and the developer roll plays a significant role in creating a uniform charge and uniform layer of toner particles across the developer roll. The charged toner particles on the surface of the developer roll are advanced towards the imaging member, and then transferred onto the imaging member in image-wise configuration to form a developed toner image on the imaging member. The toner image is subsequently transferred and fused to paper.
In the prior art, the trim blade typically comprises an angled, resilient straight edge blade urged against the surface of the developer roll along the length thereof. The trim blade consists of a metal substrate. The trim blade is oriented so that the edge portion of the trim blade contacts toner particles on the surface of the developer roll in order to smooth the layer of toner particles.
A significant disadvantage to conventional trim blades is that they deteriorate rather quickly. Particularly, the surface of the trim blade that contacts the toner particles tends to wear down over time. As the charge-metering member is responsible for creating a uniform layer of toner across the developer roll, a deteriorated or worn trim blade compromises print quality. A smooth contact surface on the trim blade is necessary to promote an even layer of toner particles. When a trim blade wears out, indicated by degradation in the quality of the final image, it is necessary for a customer to replace it with a new trim blade. Often, this involves replacing a number of system elements that are collectively provided in a Customer Replaceable Unit (CRU). When a trim blade wears out, the entire CRU must be replaced, which is an expensive and time-consuming process.
The above problem is more acute in developers employing Magnetic Ink Character Recognition (MICR) toner which toner tends to be very abrasive because of the magnetite in the toner. Applicants have found that inexpensive aluminum trim bars tend to wear out quickly causing high service cost and stainless steel trim bars have much better wear characteristics but are hard to manufacture.